Pressure variable resistance



A. CHURCHWARD.

PRESSURE VARIABLE RESISTANCE.

APPLlCATiON FILED MAY 7,1920.

- Patented Nov. 15, 1921.

2 SHEETS-SHEET I.

A. CHURCHWARD.

PREssuRE VARIABLE RESISTANCE.

APPLICATION FILED MAY 7, I920.

Patented Nov. 15, 1921.

2 SHEETSSHEET 2- W MU UNITED STATES PATENT OFFICE.

ALEXANDER CHURCI-IWARD, OF NEW YORK, N. Y.', ASSIGNOR TO WILSON WELDER 8t METALS COMPANY, INC., A

CORPORATION OF NEW YORK.

PRESSURE VARIABLE RESISTANCE.

Specification of Letters Patent.

Application filed May 7, 1920. Serial No. 379,431.

To all whom it may concern:

c it known that I, .ALEXANDER CHURCH- WARD, a citizen of the United States, residingat New York city, county of New York, State of New York, have invented certain new and useful Improvements in Pressure Variable Resistance, of which the following is a specification.

This invention relates to electric rheostat apparatus of the type employing a pressure variable compensating resistance for controlling the current in an electrical circuit.

pressure variable resistance of the above type of welding apparatus generally consists of a pile of resistance blocks, usually of carbon, arranged face to face and adapted to be variably compressed together to interpose a variable resistance to the flow of current in the circuit.

One object of this invention is to effect a better cooling of the resistance pile, in order to prevent the possibility of excessive over-heating and premature burning out of the carbon resistor units.

A further object is to provide a compensating resistance, consisting of a plurality of resistor elements, each of which consists of a block of resistance material having associated therewith a metallic heat radiating plate, said blocks being detachably carried by said plates so that they may be readily removed for replacement.

A further object is to provide the carbon blocks of said resistance units with a nonoxidizable and incombustible coating upon their exterior surface, in contact with the air, to prevent premature oxidation of said blocks.

While this invention is applicable to all types of pressure variable rheostats, it is particularly adapted for use in electric welding systems for controlling the strength of the arc current.

Further objects will appear in the accompanying description and drawings in which like reference numerals refer to like parts, and which illustrate several forms of improved resistor elements, which may be employed. i

Referring now to the drawings Figure 1 is a perspective View of one form of resistance element embodying the present invention.

Fig. 2 is a perspective view of a complete rheostat partly broken away, showing a plurality of resistance elements arranged in operating position and also showing one end of the compressing lever.

Fig. 3 is a view in elevation, of a modified form of resistance element.

Fig. 4 is a top plan view of an end tlon of a rheostat, having a resistance elements shown in ranged end to end.

Fig. 5 is a view in elevation, partly in section, of a still further modified form of resistance element.

Fig. 6 is a perspective view of one of the small carbon resistance blocks employed in the resistance element illustrated in Fig. 5.

Fig. 7 is a diagrammatic representation of the complete welding circuit, showing the generator, the solenoid controlled compressing lever, the pressure variable resistance pile and the welding electrodes.

Referring to Figs. 1 and 2 of the drawing, 1 represents a portion of the welding panel which may be composed of slate or other insulating material. Spaced apart upon the panel 1 are the supports 2 and 3, also of insulating material. Extending between and adjustably connected to said supports 2 and 3 are the cylindrical insulating rods 4, which are adapted to loosely hold the radiating plates therebetween. Any convenient number of cylindrical insulating rods 4 may be provided, but I prefer to employ four, one upon each side and two underneath the resistance elements. Said cylindrical insulating rods 4 are threaded upon their ends and extend through openings in the supports 2 and 3, being adjustably secured to said supports by means of the nuts 5.

eferring more particularly to Fig. 1, the resistance element for the pressure variable rheostat is shown as comprising the heat radiating plate 6, formed of copper or other suitable metal, preferably having a high heat conductivity. The plate 6 is provided with a rectangular recess 6 at the bottom and carries the resistance block 7, preferably of carbonaceous material such as graphitized carbon. Said block is provided with notches or grooves 8 upon both vertical side edges, and 1s preferably coated upon its exterior surfaces, which are in contact with the air, with a nonoxidizable incombustible material, such as amaterial containing silicate of soda or asbestos. The metal plates 6 function merely to radiate the heat generated in the resistance blocks and it is not necessary therefore that the plates and porplurality of the Fig. 3, and arlatentod Nov. 15, 1921. I

l)lO('l S be in perfect electrical contact. The radiating plate (3 may be plated with nickel or other metal if desired. The height oi each block 7 is less than the depth of the recess 6 in the radiating plate 6 and said block is securely but detachably held in position in said recess by means of the metal clip 9, preferably of brass having a bottom curved portion 10, and the two parallel side portions 11 and 11, the side portions 11 having indented or depressed portions 13 registering with perforations 12 in the heat radiating plate. By reason of this con struction when the clip 9 is forced over the edge of the radiating plate the indented portions 13 will come into registry with the perforations 12 and will snap tightly into place by reason of the resillency of said clip. The resistance blocks 7 will then be held detachably in position and it will be evident that they may be readily replaced whenever desired. It will be noted that the metal clips 10 which rest upon the lower insulating rods 4 are rounded so as to enable ths,1 resistor elements to slide easily upon the ro s.

Fig. 2 shows a complete rheostat with the resistance elements 6 arranged in pile formation, face to face, between the supports 2 and 3 pressure being exerted thereon by the lever 16 acting through the pin 15 and end plate 14.

As clearly shown in Fig. 7, pressure exerted by the lever 16 upon the end plate 14 of the rheostat 23 is dependent upon the opposing pulls of the solenoid 17, in series with the welding circuit, and the tension of the spring 18, the core of the solenoid being pivotally connected to said lever. The dashpot 19 which is also connected to said lever is employed to dampen somewhat the extent of its vibrations. The current is supplied to the welding circuit by means of the generator 20, of any suitable construction, and the current may be traced through the circuit as follows: from the generator 20, through the wire 21, series solenoid 17, the wire 22, carbon pile 23, wire 24, the work 25, through the are to the electrode 26, and thence back to the generator. through the wire 27 In operation, the carbon resistance blocks through which the current flows and in which the heating takes place, will be efficiently cooled by the radiation of the attached lates 6 in such a manner as to avoid all possibility of overheating. In fact, it has been found that even when large currents are sent continuously through the rheostat for long periods of time the radiation will be suflicient to maintain the blocks at a safe temperature. The coating upon said blocks assists in preventing premature oxidation and this coating will entirely prevent any objectionable effects due to convection air currents. It has been found upon actual test, that by the use of such a covering, the rheostat may continuously transmit heavy currents at a red heat without sensible disintegration of the carbon blocks and will operate quite satisfactorily even under such abnormal working conditions. Moreover, it will be evident that by locating the resistance blocks 7 in the lower part of the radiating plates close to the supports 4, pivoting or tiltin movements of said plates about their polnts of support will be eliminated. Hence in operation the resistor elements will slide along the insulated tubes 6 without pivoting, which might cause uneven contacts between the blocks.

Another advantage of the foregoing construction is that the smooth unobstructed portions of the plates are at the top, thus facilitating the radiation of heat therefrom.

The modified form of resistance unit disclosed in Figs. 3 and 4 will now be described. As is clearly shown in Fig. 3 the side frame members 31 and 32 are spaced apart and carry the upper and lower radiating plates 33, 34 therebetween; the lower plate 34 being permanently fastened to said frame members by means of the pins 40, while the upper plate 33 is loosely and slidably carried between the frame members. The upper ra diating plate 33 is provided with a plurality of recesses 35 (three in this instance) and the lower plate 34 is provided with a similar number of recesses 36 registering with the recesses 35. The carbon blocks 37 are grooved at their upper and lower edges 38 and 38 and are detachably fitted within said recesses, the grooves of said blocks fitting snugly about the edges of the thin metal plates 33 and 34. The upper plate 33, which is slidably carried within the frame members 31 and 32, is provided at its top edge with a steel clip 41 carrying a wire compression spring 39, the ends of said spring being wound about the pins 42. As will be evident the upper and lower plates are constantly pressed together by the compression of the spring 39 thereby maintaining a good electrical and heat contact between said radiating plates and the carbon blocks.

Whenever it is desired to remove any of the carbon blocks 3, as for example to replace worn blocks by new ones it will merely be necessary to slide the upper plate 33 upwardly against the compression of the spring 39 a suflicient distance to enable the carbon blocks to he slipped out of the recesses 35 and 36.

Fig. 4 illustrates the appearance of a rheostat employing the resistor elements shown in Fig. 3, the figure showing only a portion of the end of the rheostat, opposite from that at which the compression lever is located. The end plate 43, shown in Fig. 4, may be made of radiating material similar to that of 'the radiating plates 33 and 34 and may carry a plurality of thick carbon blocks 44,'generally three in number, in alinenient with the blocks carried by the resistance elements. These thick carbon blocks 44 adapted to form supports for the resistance block of the last resistance element of the series. Said carbon blocks 44 are preferably copper plated and tinned upon their back surfaces next to the end plate 43. The lower portion of the end plate 43 is preferably provided with an extension 45 to which is attached a conducting lead wire 46.

A third modification illustrating a still further form of this invention is disclosed in Fig. 5, and will now be described. In this modification, the resistance unit is shown as comprising a main heat-radiating plate 47, having three symmetrically spaced carbon block recesses 49, 50 and 51. Each carbon block is provided with grooves 54 and 55 located on two opposing edges, and said blocks are adapted to be secured detachably in position by means of the two side plates 52 and 53, formed of radiating material similar to that of the radiating plates 6, 33, 34 and 47. As shown in Fig. 5, these side plates 52 and 53 are adapted to lie upon opposite sides of the radiating plate 47 and to fit within the adjacent grooves of each of the blocks 48. The radiating plate 47 is provided with a centrally located hole 56 spaced from the three recesses 49, 50 and 51. The plates 52 and 53 are also provided with a central perforation registering with the hole 56 in the radiating plate 47. The side plates are secured to the radiating plate 47 by means of the bolt 57, held in position by the nut 58 and as will be evident the carbon blocks are thus readily replaced.

It is desired that it be understood that either of the three forms of resistance plates which have been shown by way of illustrating this invention, may be employed in any of the common pressure variable rheostats, in place of the usual resistance blocks composed entirely of carbon ordinarily employed.

It is also to be understood that this invention may be practised in various other ways, within the scope of the following claims, and that it is not to be restricted to the illustrated embodiments herein disclosed. For example, the heat radiating plates described above need not necessarily be fiat, as shown.

What is claimed is:

1. A resistor element for electric pile rheostats comprising a metallic plate having a radiating surface, said plate having a carbon resistor unit detachably carried thereby.

2. A resistance element for electric pile rheostats comprising a metallic radiating plate, said radiating plate having a block of resistance material extending through a perforation therein and readily detachable therefrom.

3. A heat condlicting plate for a resistor element for an electric rheostat, said plate being formed of two relatively 1novable parts, and having means for detachably holding a block of resistance material between said relatively movable parts.

4. A resistor element for electrical rheostats comprising two metallic plates, said radiating plates being spaced from one another in the same plane, a block of resistance material located between said plates said partsbeing resiliently and detachably held 1n operative position.

5. A pressure variable resistance having a plurality of elements, one of which comprises a plate of heat conducting material in which is detachably carried a carbon block thicker than said plate and projecting therethrough.

6. A resistor element for electric rheostats comprising a radiating plate having a rectangular notch or recess in one edge thereof, a carbon block of resistance material located in said notch or recess, and means resiliently and detachably holding said block in contact with said radiating plate.

7. A resistor element for electric rheostats comprising a radiating plate having a rectangular notch or recess in one edge thereof, a carbon block of resistance material located in said notch or recess, and a resilient metallic clip for detachably holding said block in contact with the radiating plate.

8. A rectangular block of resistance material adapted to be carried in a recess of a metallic plate of a pressure variable electric rheostat,.one of the edges of said block having a groove for fitting about the edge of the recess of said plate.

9. A rectangular block of resistance material adapted to be carried in a recess of a radiating plate of a pressure variable electric rheostat, edges of said block being grooved to fit the edges of the recess of said radiating plate.

10. In an electric rheostat, a series of carbon blocks with adjacent faces in contact in. pile formation, the exterior surface of said blocks in contact withthe air being coated with a non-oxidizable incombustible material.

11. In an electric rheostat, a series of carbon blocks with adjacent faces in contact in pile formation, the exterior surface of said blocks in contact with the air being coated with material containing silicate.

12. In an electric rheostat, the combination of end plates and side insulating retaining rods to form an inclosure, a plurality of heat radiating plates arranged between said end plates, each of said radiating plates detachably carrying a resistance block, and means for compressing the blocks to vary the resistance of said rheostat. I

13. A pressure variable resistance having a plurality of elements, one of which comprises a metal plate on which is detachably carried a carbon block the removable block slidable in the plane of said plate.

14. In a pressure variable electric rheostat for regulating the current of a welding are, a plurality of independently movable resistor elements, each resistor element comprising a radiating plate having a block of resistance material movably and detachably carried thereon, means for insulating and supporting said radiating plates, and means for compressing the resistance blocks to vary the resistance of the rheostat, by forcing the free end of said blocks to move in a direction parallel to the longitudinal axis of said rheostat.

15. A resistor element for electric pile rheostat comprising a metallic heat conducting plate, and a plurality of carbon resistor units detachably and movably carried by said radiating plate.

16. In electric rheostats a resistor element comprising a heat radiating plate, said plate having a plurality of side notches, and blocks of resistance material located in said notches.

17. In a pressure variable resistance, a

combination with a heat conducting plate havin a recess in one edge, of a carbon block slidab le in said recess, and means in cooperation with said plate for retaining the block in said recess.

18. In a pressure variable rheostat, the combination with a heat conducting plate, of a carbon block attached thereto, the edges of said block in contact with the air being coated with a non-oxidizable or incombustible material.

19. In. a pressure variable rheostat, the combination with a supporting plate, of a carbon block removably attached thereto, a guide frame member secured to said supporting plate, a second plate slidable along said guide frame member and a spring in cooperation with said guide frame and second mentioned plate for clamping the carbon block between said two plates.

20. In a carbon pile rheostat, the combination with a heat conducting plate provided with a recess in one edge of a carbon block slidable in said recess and projecting onboth sides of said plate, and removable means in cooperation with said plate and the outer edge of the carbon block for retaining said block in said recess.

In testimony whereof, I have affixed my signature to this specification.

ALEXANDER CHURCHWARD. 

